For her performance as sado-masochistic Viennese piano instructor Erika in director Michael Haneke's forceful, tortuous film, Isabelle Huppert won the best-actress award at last year's Cannes Film Festival, and deserved it. Huppert is a star of the French cinema, with credits that range from soap opera to costume epic to nihilistic modern tragedy. But she's never done a more fearless piece of work than embodying Erika, a respected conservatory teacher with a mean streak that hides a vein of self-loathing and a perverse secret life. Locked in a needy, hate-fueled relationship with her overbearing mother (veteran French actress Annie Girardot), Erika seeks release through a mutual attraction with Walter  a handsome, narcissistic student played by Benoit Magimel (named best actor at Cannes for the role). Warning: The taboo situation  teacher/student, older woman/younger man  is exacerbated by Erika's bondage fantasies and aberrant behavior, and may alarm some sensitive viewers.